The first three influence SP and thus the score you get, the other five can give you up to 5 extra power stars per power, so the key is to distribute these powers accordingly to compensate for the stuff you can't do. In general, the first song is much easier to do than the second one, so you should put the powers which make it harder to get power stars on the first song, and the 'easier' ones on the second song.

I did it like this, since I find the second song much harder to combo.First song:- Streak Guardian- Multiplier Extender- Star Power Generator- Speed Freak

After this, you'll need to beat one more song with all eight powers combined, which shouldn't prove too hard. Just keep trying for that one: I really can't add anymore than that since I didn't have too much trouble beating the final song.